Machines for machining workpieces with tools are known in the field of mechanical engineering and tool making as what are referred to as machine tools. According to a narrower interpretation, this term is used primarily in the context of joining, shaping and separating production processes, in the last-mentioned case in particular cutting, machining and subtractive production processes within the meaning of the Standards DIN 8580 et seq. and DIN 69 651, Part 1. This more restrictive definition is now also used as the basis for the following statements.
With the aim of shaping the workpiece, a generic machine tool creates a relative movement between the tool and workpiece, this relative movement being able to be subdivided functionally into an advancing or infeed component and a main component. The most important structural component of modern machine tools is in this case a direct-drive, precisely mounted shaft having a usually integrated tool interface, these being familiar to a person skilled in the art as motor spindles.
Although said relative movement between the tool and workpiece can be brought about in principle by means of a rotation of either of the two elements, drilling, grinding and milling machines according to the prior art are usually equipped with tool-carrying motor spindles which are denoted tool spindles in the following text. DE 101 37 437 B4 describes for example a machining process based on such a drill spindle for bores such as the pin bore of a piston or the connecting-rod bore of a connecting rod, and in this context the pin bore or the connecting-rod bore is machined with a drill spindle of a machining device and the drill spindle is arranged in an offset manner with respect to the theoretic hole center of the bore during the machining operation, and the piston or the connecting rod executes a linear movement in the advancing direction during the machining operation.
Especially nonround bores, for example what are referred to as spherical bores, prove to be problematic here. A precision drilling machine intended to produce such bores is disclosed for instance in DE 44 42 218 A1. According to that proposal, the precision drilling machine is intended to be equipped with a drill bit on a drill spindle and with a holder for a workpiece to be machined in order to produce nonround bores for economical use at high rotational speeds. For this purpose, the holder for the workpiece oscillates in translational movement in at least one direction with a frequency determined by the particular rotational speed of the drill bit and on a deviation path determined by the bore shape to be produced.
DE 10 2008 063 945 A1 also relates to a process for forming nonround bore profiles and concentrates in this case on pin bores of pistons of an internal combustion engine, which are intended for receiving bearing bushes. Machining takes place in this process by means of a rotating and linearly displaceable drill rod that is guided through the pin bores and is received between a fixed centering point and a movable centering point, and an associated cutting tool. The movable centering point is in this case assigned to a rocker arm of an electronic shaping bolo head, via which the drill rod is movable so as to oscillate and/or be pivotable to a limited extent during the machining operation to create geometrically differently shaped bore profiles of the pin bores.
DE 10 2005 020 501 A1 describes a similar process for introducing a nonround pin bore into a piston of an internal combustion engine by means of a rotating and linearly displaceable drill rod. According to that approach, provision is made for the drill rod to be mounted between a fixed and a movable center and for the nonround form that is to be introduced to be scanned by means of a rocker lever and transmitted to the drill rod.
According to the process explained in DE 103 08 442 B3, by contrast, in order to produce a shaped bore by subtractive machining, a tool is driven by means of a magnetically mounted spindle that is drivable in rotation. The tool is mounted on that side of the workpiece that is remote from the spindle by a radially-magnetically mounted counter spindle. The radial position, the axial position and the angular position of the spindle are sensed by radial sensors, axial sensors and an angular position encoder and regulated to a programmable setpoint value via a regulating system. The workpiece and the tool are movable with respect to one another in the axial direction.
Finally, WO 2011/005498 A2 should also be acknowledged, said document proposing a further process for shaping pin holes and a corresponding drilling system. The process and device comprise in this case the fastening of a piston to a holder supported by a slide. Then, a cutting element rotates about a first axis and the slide, together with the holder, moves along the first axis in the direction of the cutting element and brings the piston into cutting contact with the cutting element. Furthermore, the holder moves along second and third axes which each extend transversely to the first axis, and the cutting element works the desired pin-hole contours into the piston.